This invention relates to a heat resistant resin composition excellent in heat resistance and storage stability used for supporting films and the like formed articles and to an insulated wire obtained by using said resin composition.
Polyamide-imide resins are well known as being excellent in heat resistance, chemical resistance and mechanical properties and widely used as varnishes for heat resistance wires, varnishes for protecting metal surfaces, films, laminates, adhesives, powder molding materials and the like. Processes for producing polyamide-imide resins are also known (e.g., Japanese Patent Appln. Kokoku (Post-Exam Publn) No. 19274/69). But, resulting resin compositions sometimes increase their viscosities with the lapse of time depending upon production conditions, which results in lowering in so-called storage stability. When a resin composition increases its viscosity with the lapse of time, there arise many inconveniences in that, for example, in the case of using said resin composition as a varnish for protecting metal surfaces, it is necessary to modify coating conditions initially settled, it is necessary to adjust the viscosity of said resin composition having increased viscosity by diluting it with a solvent, and the like and that various properties of the resulting protective coating film obtained by evaporating the solvent are sometimes changed undesirably. Particularly, in the case of applying these resin compositions to circuit boards for electronic parts, changes in viscosity bring about serious problems since very thin films such as those having a few microns in thickness should be formed.